Many chemical carcinogens undergo metabolic change within the body cells, some of which result in conversion to the active, carcinogenic forms. They are then further modified to inactive forms. These changes are controlled by a variety of enzymes. We study certain of these enzymes, particularly with reference to genetic variation in the enzyme activities and relationship of such variation to susceptibility and/or resistance to the carcinogens. The active products are detected by chemical methods and also by bioassay methods which depend on the fact that they are active mutagens. Emphasis is on application of the work to human cancers. Use of genetically variant enzymes as genetic markers, based on detection by zone electrophoresis techniques. Such markers are employed in several different projects including: 1. Control of gene expression in hybrid frog embryos. 2. Abnormal enzyme types produced by bacteria containing nonsense suppressor mutations. 3. Comparative enzymology of various taxa, in the development of a quantitative taxonomy. 4. Genetic differences in isozymes between fish of the genus Xiphophorus, with particular reference to genetic divergence in evolution. 5. Induction and electrophoretic detection of mutations in mammalian cell lines, with particular reference to development of sensitive detection systems for environmental carcinogens and mutagens. BIBLIOGRAPHIC REFERENCE: Shaw, Charles R. The microsomal mixed function oxidases and chemical carcinogens. 1975. In Isozymes III, Developmental Biology, ed. C. Markert, Academic Press, N. Y., pp 809-918.